In the manufacturing of semiconductor devices, etc. used in electronics technologies leading information-oriented society, silicon wafers may not be omitted. Characteristics of silicon wafers include micro defects such as oxygen precipitate, dislocation, oxygen stacking faults and the like. Micro defects are advantageous for capturing heavy metal pollution that occurs in a device process, but may become a source of device failure. Therefore, there may be a need to adjust the oxygen concentration in a crystal to a predetermined concentration corresponding to types of devices or device processes used.
As a current method of manufacturing silicon single crystals, the “Czochralski method” (hereinafter referred to as “CZ method”) of manufacturing silicon single crystals through pulling is generally used. In addition, there is a method called the magnetic field applied Czochralski method (MCZ method) which is a CZ method peformed under a strong magnetic field. The CZ method includes a magnetic field applied Czochralski (MCZ) method in which a strong magnetic field is formed.
In the CZ method, a polycrystalline silicon that is highly purified with a metal impurity concentration of a few ppb (parts-per-billion, 1 ppb=10−9) or less is generally put into a high-purity vitreous silica crucible together with a resistivity control dopant (e.g., boron (B) or phosphorous (P)) and is melted at a temperature of about 1,420 deg. C. Continuously, a seed crystal silicon rod is brought into contact with a surface of silicon melt, the seed crystal or the vitreous silica crucible is rotated to make the seed crystal thin (dislocation-free) and then the seed crystal is pulled, thereby enabling a silicon single crystal ingot having the same atomic structure as the seed crystal to be obtained.
As aforementioned, the vitreous silica crucible is a container to put silicon melt therein when pulling molten polycrystalline silicon into a single crystal. The amount of the silicon melt in the vitreous silica crucible is decreased in inverse proportion to the amount of silicon single crystal pulled, and the level of the surface of the silicon melt (hereinafter referred to as “melt surface”) is changed in the vitreous silica crucible. It is general practice to directly observe and monitor the changing level of the melt surface, but such direct observation has the problem in that the decrease in volume of the silicon melt cannot be accurately measured.
Recently, silicon single crystal ingots have been advanced to a large diameter (of 300 mm or more). The large diameter of the silicon single crystal ingot is problematic in that the phenomenon can easily occur in which the melt surface of the silicon melt sloshes (vibrates) between a portion where a neck part is formed and a portion where a shoulder part is formed, for a duration of a few minutes to a few hours. As a countermeasure to the foregoing problem, methods for preventing vibration of the melt surface have been considered, such as a method of applying a magnetic field to the melt surface through the foregoing MCZ method, a method of providing a region, called a special region, in the vitreous glass crucible for preventing the sloshing of the melt surface, or the like. However, a method of completely preventing the vibration of the melt surface under any pulling condition has not yet been found. Therefore, even in the case where the melt surface is disposed in the special region, a countermeasure that is employed is one where the pulling rate is decreased during a period in which vibration of the melt surface is easily generated.
In a conventional vitreous silica crucible, even though the foregoing special region is provided, the special region cannot be discerned by its appearance. Also, since a carbon susceptor supporting the vitreous silica crucible reacts with an outer surface of the vitreous silica crucible during the pulling of a silicon single crystal, so that an inner diameter of the carbon susceptor is changed whenever the carbon susceptor is used, initial melt surfaces are not always at the same level, although silicon raw material is filled by the same weight in the vitreous silica crucible. Therefore, although a distance between an initial melt surface level and a melt surface level changed during pulling is known, a relative position between the melt surface and the special region provided in the vitreous silica crucible cannot accurately be known.
That is, for example, although the sloshing of the melt surface disappears, and the seed crystal arrives at a region beyond the special region and may increase the pulling rate of a silicon single crystal, it may not be determined whether the sloshing disappears due to an effect of the special region or whether a region is one which may increase the pulling rate, and in a real process, it is problematic that the pulling rate of silicon single crystal may not be increased. In relation to this problem, patent document 1 below discloses that a position measuring apparatus is provided at a side of a single crystal pulling apparatus.